Alcoa boffins develop new low cost technology to reduce smelter emissions

The Alcoa Technical Center (ATC) has developed technology that uses 50% less water and 30% less energy and will reduce emissions at a fraction of the cost of current technology in the field.

ATC will complete commissioning and on-site testing of its In-Duct Scrubber in August 2014 and plans to commercialise the technology, says Ray Kilmer, Alcoa's executive vice president and chief technology officer.

The new In-Duct scrubber is currently under construction as part of a commercial-scale demonstation project at Alcoa's Lake Charles, Louisiana-based baked anode and calcined coke facility in the USA.

Alcoa’s Lake Charles plant makes baked carbon anodes and calcined coke for use in smelting operations. The plant has an annual production capacity of 283kt of calcined coke and 138kt of carbon anodes, and employs 182 people. The In-Duct Scrubber pilot project will create 40 construction jobs over the next 12 months.

Compared to traditional wet scrubbers originally developed to reduce emissions at power plants and large industrial facilities, Alcoa's pantented technology has the ability to dramatically reduce scrubber installation costs and reduce operating costs by approximately one-third, claims the company. This is due to improved processes and increased energy efficiencies. The new system is claimed to use 50% less water and consumes 30% less energy.

According to Kilmer, "Alcoa's experts have extended the boundary of traditional scrubbing equipment, enabling a more cost effective, robust and sustainable alternative for reducing industrial emissions."

Conventional scrubbers, suitable primarily for large power plants, are 100-to-150ft tall towers and require significant capital to construct and energy to operate. They pump a limestone or sodium-based solution to the top of the tower and spray it onto flue gas, which is then propelled from the bottom to the top of the building and uses 50% more water and 30% more energy than Alcoa’s new technology. 

The In-Duct Scrubber was designed to reduce sulfur dioxide and particulate matter emissions generated from smelters and moves flue gas from the smelter into a horizontal chamber prior to spraying a sodium-based solution onto the gas stream in the same direction as the gas flow. The sodium-based solution reacts with the sulfur dioxide in the flue gas and turns it into water and sodium sulfate.  When mixed with lime, sodium sulfate produces a gypsum by-product, which can be used to make various  products such as wallboard and additives for cement making.

The new process allows up to three times more gas to be treated than in an equivalent conventional scrubber space and treats upwards of 90% of sulfur dioxide in less than one-fifth of a second compared to traditional wet scrubbers, which could take 10-15 seconds. The modular technology requires less physical space than conventional systems.